METHOD AND APPARATUS FOR THE SECRET TRANSMISSION OF SPEECH SIGNALS

摘要

1479717 Secret signalling PATELHOLD PATENTVERWERTUNGS & ELEKTROHOLDING AG 10 June 1974 [12 June 1973] 25576/74 Heading H4R In a method and apparatus for the secret transmission of speech signals by coding in the transmitter and decoding at the receiver gaps due to pauses are at least partially filled after the encoding stage by the addition of encoded filler signals and are subsequently suppressed in the receiver. The filler signals may fill the gaps or may do so jointly with encoded control signals indicative of the respective gaps. The filler signals encoded from a noise generator may be applied by way of relay contacts and may be placed relative to the speech signals by appropriate delay networks or by the use of appropriate relay holding times. The filling may be achieved by re-reading the contents of a circulating store. The filling may be controlled by a speech detector or by a manually operated button and corresponding control signals delayed as necessary to compensate for delay in other units may be sent over a separate line or as part of a composite signal to achieve synchronization. The filler signal should have a spectrum also encountered in the encoded speech signal. Coding methods exemplified include varying the amplitude of samples, scrambling partial frequency bands and time transposing message portions. The encoded control signals may be encoded by irregular polarity reversals or may comprise keyed tones in a frequency gap in the encoded speech. The onset and termination of speech, may be transmitted by pulse trains in the gaps.